Auto-trilevel Ventilator for Patients With Overlap Syndrome

The contradiction in treatment for overlap syndrome is how to improve hypercapnia because of narrower difference between inspiratory positive airway pressure (IPAP) and expiratory positive airway pressure (EPAP), and meanwhile to eliminate apnea and popnea events which may easily occur at the end of expiration For ordinary Bipap ventilator. If the IPAP is set to higher, the patients may feel discomfort, if the pressure difference between IPAP and EPAP is too narrow or the expiratory positive airway pressure (EPAP) too high, hypercapnia may occur. If the EPAP is too low, redusual apnea and hypopnea event may become common. Auto-trilevel ventilation, with a lower airway pressure at the beginning of expiration to prevent hypercapnia and a higher airway pressure at the end of expiration to prevent residual apnea events, should be able to provide a novel ventilation mode with a higher efficacy and lower average airway pressure for overlap syndrome. To prove the hypothesis, comparison is made between ordinary BiPAP and auto-Trilevel ventilation modes during treatment for patients with overlap syndrome. In this study, the investigators compare the changes of related indexes including apnea hypopnea index、minimal pulse oxygen saturation、arousal index, sleep quality,PaCO2 and sleepiness scores) before and on treatment. Meanwhile, curative effects will be compared between BiPAP and auto-Trilevel ventilation modes. The investigators will analyze the changes and then confirm our hypothesis.